1. Technical Field
The present disclosure relates to an evaporator and a Rankine cycle system.
2. Description of the Related Art
It has been disclosed that an evaporator of a Rankine cycle system includes a working fluid passage having three zones of a superheater zone, an evaporator zone, and a preheater zone for keeping a working fluid from being excessively heated and degraded. FIG. 5 is a schematic diagram of an evaporator disclosed in Japanese Unexamined Patent Application Publication No. 2011-64451.
As illustrated in FIG. 5, a direct evaporator apparatus 260 includes a housing 244 having a heat source gas inlet 236 and a heat source gas outlet 238. A heat exchange tube 252 is disposed entirely within a heat source gas passage 246. The heat source gas passage 246 is space within the interior of the direct evaporator apparatus 260 that is not occupied by the heat exchange tube 252. The heat exchange tube 252 is configured to accommodate an organic Rankine cycle working fluid 212 such that, during operation, the working fluid enters and exits the housing 244 only twice: once as the working fluid enters the direct evaporator apparatus 260 via a working fluid inlet 240 and once as the working fluid exits the direct evaporator apparatus 260 via a working fluid outlet 242.
The working fluid travels along a working fluid passage defined by the heat exchange tube 252. With the exception of portions 250 of the heat exchange tube 252, the heat exchange tube 252 lies within the heat source gas passage 246. The heat exchange tube 252 defines three zones: a first zone 220 (preheater zone) adjacent to the heat source gas outlet 238, a second zone 222 (evaporator zone) adjacent to the heat source gas inlet 236, and a third zone 224 (superheater zone) disposed between the first zone 220 and the second zone 222. The first zone 220 is not in direct fluid communication with the third zone 224. The working fluid inlet 240 is in direct fluid communication with the first zone 220. The working fluid outlet 242 is in direct fluid communication with the third zone 224. The heat exchange tube 252 includes a plurality of bends in each of the first zone 220, the second zone 222 and the third zone 224. The heat exchange tube 252 is configured in parallel rows in each of the first zone 220, the second zone 222, and the third zone 224. Each of the first zone 220, second zone 222, and third zone 224 of the heat exchange tube 252 is configured in at least one row.
During operation of the direct evaporator apparatus 260 illustrated in FIG. 5, a heat source gas 216 entering at the heat source gas inlet 236 first encounters the second zone 222. Heat from the heat source gas 216 is transferred to the working fluid 212 present in the second zone 222. A heat source gas having a relatively lower temperature and heat content than the heat source gas 216 entering the direct evaporator apparatus 260 at the heat source gas inlet 236 next encounters the third zone 224 in which the working fluid is superheated and a superheated working fluid 228 exits the direct evaporator apparatus 260 via the working fluid outlet 242. A heat source gas having a relatively lower temperature and heat content than the heat source gas first encountering the heat exchange tube 252 in the third zone 224 next encounters the first zone 220 in which the working fluid 212 in a liquid state enters at the working fluid inlet 240 and is preheated while still in a liquid state. The working fluid in the first zone 220 is conducted along the heat exchange tube 252 to the second zone 222 in which the working fluid is evaporated and supplied to the third zone 224.